This invention relates to spark ignition gas burner control systems which utilize a microcomputer.
Due to the ever-increasing need for conservation of energy, it has become desirable, and in some cases mandatory, that the conventional standing pilot used in appliances such as furnaces be replaced with some type of interrupted ignition means. Accordingly, there have been developed systems which retain the pilot burner but provide for ignition of the pilot burner only on a call for heat, and systems which eliminate the pilot burner and provide for direct ignition of the main burner. In either system, the ignition means is generally either some type of spark ignition means or some type of hot surface ignition means.
In recent years, many such interrupted-ignition types of gas burner control systems have been developed, and some of them include a microcomputer. An example of a microcomputer-based interrupted-ignition type of gas burner control system, wherein the ignition means is a hot surface igniter, is shown and described in U.S. Pat. No. 4,518,345; an example of a microcomputer-based interrupted-ignition type of gas burner control system, wherein the ignition means is a spark, is shown and described in U.S. Pat. No. 4,581,697.
The microcomputer not only enables a considerable cost savings over discrete electrical components in providing the desired system functions, but also provides improved levels of safety, reliability, and versatility. However, a particular problem exists when using a microcomputer in systems wherein the ignition means is a spark, and more particularly, when the microcomputer and the spark transformer are located in the same physical package.
Specifically, the architecture of a typical microcomputer chip is such that the I/O (input/output) ports can be affected by electrical noise. More specifically, the spark transformer in the spark generating circuit acts as a transmitter of electrical noise, and the electrical leads or pins at the I/O ports of the microcomputer act as receivers of such noise. Such electrical noise can change the port status from its designated status to the opposite status, that is to say, from an input to an output or from an output to an input. Noise can also change the data in the port. Obviously, such changes in status and/or data, if not corrected, could cause erroneous system operation. While various hardware means can be used to reduce the transmission and/or reception of such noise, such hardware means do not ensure that the microcomputer has not been adversely affected.
Another particular concern in interrupted-ignition systems wherein the ignition means is a spark is to ensure that sparking is inhibited at all times when gas is not flowing. For example, it is imperative that sparking be inhibited during the time that the combustion chamber is being purged of any unburned fuel that may have accumulated due to an unsuccessful attempt at ignition.